Subject information acquisition device

ABSTRACT

A subject information acquisition device includes a first holding member that holds a subject of a patient, a first probe that detects an acoustic wave having propagated through the first holding member and that performs a scanning operation, a first holding-member support located on a patient side from a scanning range of the first probe and that reduces bending of the first holding member, and a second probe located on the patient side from the scanning range of the first probe.

TECHNICAL FIELD

The present invention relates to a subject information acquisitiondevice using an acoustic wave.

BACKGROUND ART

In the medical field, research is being actively pursued on opticalimaging devices that irradiate a living body with light from a lightsource, such as a laser, and visualize information about the inside ofthe living body acquired based on the light that has entered.Photoacoustic imaging is one of these optical imaging technologies. Inphotoacoustic imaging, a living body is irradiated with pulsed lightgenerated from a light source. Acoustic waves (typically ultrasonicwaves) generated from biological tissues that have absorbed the energyof the pulsed light having propagated and diffused inside the livingbody are detected. Based on the detected signal, information about theinside of the living body is visualized. Specifically, by utilizing adifference in the light-energy absorption rate between a target part,such as a tumor, and the other tissues, an acoustic wave detectordetects elastic waves generated when the target part instantaneouslyexpands in response to absorption of the energy of the irradiated light.By mathematically and analytically processing this detected signal, adistribution of optical properties inside the living body or informationrelated to the distribution of optical properties, particularly, adistribution of initial sound pressures, a distribution of opticalenergy absorption densities, and a distribution of optical absorptioncoefficients, and so forth, can be acquired.

In photoacoustic imaging, it is necessary to stably maintain the shapeof a subject during measurement in order to acquire appropriate images.Thus, PTL 1 illustrated in FIG. 10 discloses a technique for stablymaintaining the shape of a subject to acquire information about thesubject. Specifically, PTL 1 discloses a technique for stablymaintaining the shape of a subject by holding the subject between twopress plates 2 a and 2 b, and for receiving acoustic waves by performingscanning with one acoustic wave receiver 5. In addition, in PTL 1, thepress plate 2 b is used as a scanning surface of the acoustic wavereceiver 5.

CITATION LIST Patent Literature

PTL 1 Japanese Patent Laid-Open No. 2011-125571

As described above, in PTL 1, a subject is held by using holdingmembers, such as press plates, whereby an appropriate image is acquired.

However, it is desired for subject information acquisition devices toacquire higher-quality images than those acquirable with PTL 1.

Accordingly, according to aspects of the present invention, a subjectinformation acquisition device stably maintains the shape of a subjectand acquires high-quality images.

SUMMARY OF INVENTION

According to an aspect of the present invention, a subject informationacquisition device includes a first holding member arranged to hold asubject of a patient, a first probe configured to detect an acousticwave having propagated through the first holding member and to perform ascanning operation, a first holding-member support located on a patientside from a scanning range of the first probe and configured to reducebending of the first holding member, and a second probe located on thepatient side from the scanning range of the first probe.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a subject information acquisitiondevice according to a first exemplary embodiment.

FIG. 2 is a diagram illustrating a processing flow of a subjectinformation acquisition method according to the first exemplaryembodiment.

FIG. 3 is a diagram illustrating another processing flow of the subjectinformation acquisition method according to the first exemplaryembodiment.

FIG. 4A is a diagram illustrating an example of arrangement of a probeaccording to the first exemplary embodiment.

FIG. 4B is a diagram illustrating an example of arrangement of the probeaccording to the first exemplary embodiment.

FIG. 5 is a schematic diagram of a subject information acquisitiondevice according to a second exemplary embodiment.

FIG. 6 is a schematic diagram of a subject information acquisitiondevice according to a third exemplary embodiment.

FIG. 7 is a schematic diagram of a subject information acquisitiondevice according to a fourth exemplary embodiment.

FIG. 8 is a schematic diagram of a subject information acquisitiondevice according to a fifth exemplary embodiment.

FIG. 9 is another schematic diagram of the subject informationacquisition device according to the fifth exemplary embodiment.

FIG. 10 is a diagram illustrating a configuration of a measuring deviceaccording to the related art described in PTL 1.

FIG. 11 is a schematic diagram of a subject information acquisitiondevice including a holding-member support according to a comparativeexample.

DESCRIPTION OF EMBODIMENTS

In the technique disclosed in PTL 1, when the shape of a subject ismaintained by using press plates serving as holding members, the holdingmembers bend due to elasticity of the subject.

Accordingly, as in a subject information acquisition device according toa comparative example illustrated in FIG. 11, a holding-member support60 that reduces bending of a holding member 50 for maintaining the shapeof a subject 21 may be placed on a patient-20 side of the holding member50. The subject information acquisition device illustrated in FIG. 11includes a scanning probe 30 configured to perform a scanning operation,the holding member 50, and the holding-member support 60. “Patient”indicates the whole living body, whereas “subject” indicates part (suchas breast) of the living body, i.e., part to be examined. “Patient side”indicates a direction from the scanning probe 30 towards a non-subjectpart of the patient. For example, the “patient side” of theholding-member support 60 indicates, in FIG. 11, the direction above theholding-member support 60 on the paper.

The subject information acquisition device according to the comparativeexample illustrated in FIG. 11 can visualize light absorbers existing ina first detection region 101, i.e., a region where the scanning probe 30can detect acoustic waves. However, the holding-member support 60 limitsthe scanning range of the scanning probe 30, and thus there is a blindregion 103, i.e., a region where the scanning probe 30 is unable todetect acoustic waves. That is, a limited range of the angle of view ofthe probe results in light absorbers existing in the blind region 103not being visualized.

Accordingly, one aspect of the present invention provides a subjectinformation acquisition device that includes a feature in which a probeother than a scanning probe is located on the patient side from thescanning range of the scanning probe.

Exemplary embodiments of the present invention will be described belowwith reference to the drawings. Similar components are generallyassigned the same references and a description thereof will be omitted.

First Exemplary Embodiment

FIG. 1 is a schematic diagram of a subject information acquisitiondevice according to a first exemplary embodiment. The subjectinformation acquisition device illustrated in FIG. 1 includes, as basichardware components, a scanning probe 30 serving as a first probeconfigured to perform a scanning operation, a probe 40 serving as asecond probe, a first holding member 50, a first holding-member support60, and a signal processor 80. The subject information acquisitiondevice further includes a second holding member 51 positioned so as toface the first holding member 50, and a second holding-member support61. Here, each “probe” includes an acoustic wave detector that detectsacoustic waves, a control unit of the acoustic wave detector, and ahousing enclosing these components.

As illustrated in FIG. 1, in the subject information acquisition deviceaccording to this embodiment, the probe 40 is located on the patientside from the scanning range of the scanning probe 30 and above thescanning probe 30.

In this embodiment, a subject 21 is irradiated with light 10 emittedfrom a light source. Light absorbers 22(a) and 22(b) inside the subject21 absorb the light 10, thereby generating acoustic waves 23(a) and23(b). The scanning probe 30 detects the acoustic wave 23(a) generatedat the light absorber 22(a) existing in a first detection region 101,via the holding member 50. In addition, the probe 40 detects theacoustic wave 23(b) generated at the light absorber 22(b) existing in asecond detection region 102. The signal processor 80 then generatescombined image data of image data corresponding to a signal detected bythe scanning probe 30 and image data corresponding to a signal detectedby the probe 40. The combined image data is displayed on a displaydevice 90.

As described above, this embodiment includes a feature in which theprobe 40 is located on the patient side from the scanning probe 30 anddetects the acoustic wave 23(b) generated at the light absorber 22(b)existing in the second detection region 102. This enables visualizationof a region that is unable to be visualized with a configuration inwhich acoustic waves are detected only with the scanning probe 30.

In this embodiment, a pressing mechanism 53 moves the first holdingmember 50 and the second holding member 51 to hold the subject 21therebetween, whereby the shape of the subject 21 is maintained. In thismanner, the thickness of the subject can be reduced, and thus light islikely to reach a light absorber at a deep part of the subject. It isnot necessary to hold the subject from both sides as long as the shapeof the subject can be maintained only with the first holding member 50.That is, the subject information acquisition device need not include thesecond holding member 51, the second holding-member support 61, and thepressing mechanism 53.

Also in the subject information acquisition device according to thisembodiment, a patient support 63 that supports a patient 20 is locatedbetween the patient 20 and the probe 40. However, subject informationacquisition devices of certain types, such as standing and seated types,need not include the patient support 63 because the applied weight ofthe patient is small.

In addition, a detection surface of the probe 40 may be appropriatelyset in a desirable direction for detecting acoustic waves.

Moreover, when acoustic impedance matching is desired between thesubject 21 and another member, an acoustic matching material, such asultrasound gel, water, or mineral oil, may be used.

Subject information acquisition methods performed by the signalprocessor 80 will be described below. Numerals below match numerals ofprocesses illustrated in FIGS. 2 and 3.

First, the subject information acquisition method illustrated in FIG. 2will be described.

Process 1 (S111, S112): Process of Detecting Acoustic Waves with probesand acquiring electrical signals

In this process, the subject 21 is irradiated with the light 10, and thescanning probe 30 and the probe 40 detect the acoustic waves 23(a) and23(b) generated at the light absorbers 22(a) and 22(b) in the subject toacquire electrical signals. At this time, the scanning probe 30 detectsthe acoustic wave 23(a) generated at the light absorber 22(a) existingin the first detection region 101, via the holding member 50. Also, theprobe 40 detects the acoustic wave 23(b) generated at the light absorber22(b) existing in the second detection region 102.

At this time, the acoustic waves can be detected with the scanning probe30 and the probe 40 by irradiating the entire subject 21 with light.

Alternatively, the first detection region 101 and the second detectionregion 102 may be separately irradiated with light and the probescorresponding to the regions may detect acoustic waves generated in theregions. Accordingly, even if an insufficient amount of light isradiated to a wide range at one time, sufficient amounts of light can beensured in the regions when the regions are separately irradiated withlight. At this time, the order in which the regions are irradiated withlight does not matter. Also, the regions may be individually irradiatedwith light at the same time.

Process 2 (S121): Process of Converting Electrical Signals into DigitalSignals

In this process, a signal collector 70 amplifies the electrical signalsacquired in S111 and S112, and converts the electrical signals intodigital signals. In addition, the digital signal is recorded in a memoryof the signal processor 80 in association with the position of anelement that has acquired the digital signal.

When detection is performed at the same position a plurality of times,signals detected at the same position may be simply added as well asaveraged after completion of the detection.

In the case of an element not working properly or a probe with a sparsearray, a missing signal corresponding to the position may beinterpolated by newly creating a signal based on the signals fromsurrounding positions. For example, the missing signal may beinterpolated by averaging signals from elements adjacent to the positionwithout the detection element, or the missing signal may be interpolatedby shifting an original signal in the time domain taking into accountthe phase to perform averaging and create a pseudo-signal.

This process can be omitted when the following process is performed onthe electrical signals, i.e., analog signals.

Process 3 (S131): Process of Combining Detected Signals

In this process, the signal processor 80 combines detected signals.Here, the detected signals are concepts including the electrical signalsacquired in S111 and S112 and the digital signals acquired in S121.

At this time, when there is a signal transmission medium, such as thefirst holding member 50, between the scanning probe 30 or the probe 40and the subject 21, and the speed of the sound propagating in thesubject 21 differs from that in the signal transmission medium, thedetected signals are combined taking into account the signal acquisitiontiming lag due to the signal transmission medium. For example, in onecase, the first holding member 50 is located between the scanning probe30 and the subject 21 while the probe 40 is directly in contact with thesubject 21. In this case, prior to combining, the signal from the probe40 is delayed, assuming that the first holding member 50 is locatedbetween the probe 40 and the subject 21. Alternatively, a signalobtained by taking into account the first holding member 50 is removedfrom the signal of the scanning probe 30 before the detected signals arecombined.

When the probes have different element widths or center frequencies, thedetected signals may be combined, taking into account thecharacteristics of the probes, such as the element widths and thedirectivities.

When a signal corresponding to a specific position is missing in thecombined signal, the missing signal may be interpolated by newlycreating a signal based on the signals from the probes. For example, themissing signal can be interpolated by averaging signals from elementsadjacent to the position without the element or by shifting an originalsignal in the time domain taking into account the phase to performaveraging and create a pseudo-signal.

Process 4 (S141): Process of Generating Image Data from CombinedDetected Signal

In this process, the signal processor 80 performs image reconstructionbased on the combined detected signal generated in S131 to generateimage data of the inside of the subject. In this process, since imagereconstruction is performed based on the combined detected signal,combined image data of image data corresponding to the signal detectedby the scanning probe 30 and image data corresponding to the signaldetected by the probe 40 can be generated. Here, the image datarepresents a distribution of optical properties inside the subject orinformation related to the distribution of optical properties,particularly, a distribution of initial sound pressures, a distributionof optical energy absorption densities, a distribution of absorptioncoefficients, and so forth.

Next, the subject information acquisition method illustrated in FIG. 3will be described. Processes similar to those in FIG. 2 are assigned thesame processing numerals and a detailed description thereof will beomitted.

The subject information acquisition method illustrated in FIG. 3 differsfrom the subject information acquisition method illustrated in FIG. 2 inthat pieces of image data for the scanning probe 30 and the probe 40 aregenerated based on the detected signals obtained by the respectiveprobes and then the pieces of image data are combined.

Process 3 (S231, S232): Process of Generating Pieces of Image DataCorresponding to Detected Signals

In this process, the signal processor 80 generates image datacorresponding to a signal detected by the scanning probe 30 and imagedata corresponding to a signal detected by the probe 40 based on therespective detected signals. At this time, image reconstruction isperformed, taking into account the characteristics of the probes, suchas the element width and the directivity, and the characteristics of theholding member.

Process 4 (S241): Process of Combining Pieces of Image Data

In this process, the signal processor 80 combines the image data,generated in S231, corresponding to the signal detected by the scanningprobe 30 and the image data, generated in S232, corresponding to thesignal detected by the probe 40. At this time, the signal processor 80can combine the pieces of image data, taking into account the capturingpositions and voxel sizes of two images, the sizes of the elements, thedirectivities, and the center frequencies. A case of probes havingdifferent center frequencies will be described below.

In general, an image acquired with a probe having a high centerfrequency has a high resolution in a direction perpendicular to thedetection surface of the probe. That is, since images obtained withprobes having different center frequencies have different resolutions,an image obtained by simply combining these images is unnatural.

Accordingly, the images are combined after converting the resolution ofthe image acquired with the probe having the higher center frequency tomatch the resolution of the image acquired with the probe having thelower center frequency. In this way, unnaturalness of the combined imageis reduced. Examples of the resolution matching method include, but arenot limited to, averaging absorption coefficients in directionsperpendicular to the detection surfaces of the probes or applying afiler.

The subject information acquisition methods illustrated in FIGS. 2 and 3can also be similarly performed in subject information acquisitiondevices according to embodiments described below.

Components of the subject information acquisition device will bedescribed below.

(Light Source)

As the light source, a pulsed light source capable of generating lightpulses of the order of several to several hundred nanoseconds may beused. Specifically, a pulse width of approximately 10 nanoseconds isused to efficiently generate acoustic waves. While a laser may be usedto obtain a high output, a light-emitting diode or the like may also beused instead of the laser. Various types of lasers, such as asolid-state laser, a gas laser, a dye laser, or a semiconductor lasermay be used. Timing, waveform, and intensity of radiation are controlledby a light-source control unit (not illustrated). In addition, the lightsource may be capable of performing scanning so as to irradiate a widerange of the subject 21 with light. Also, the light source may beintegrally provided in the subject information acquisition device orseparately provided as another device. Furthermore, a plurality of lightsources for respective probes may be provided in order to irradiaterespective detection regions of the scanning probe 30 and the probe 40with light. Moreover, a combination of an optical fiber, an opticallens, and a prism can be used as an optical system from the light sourceto the radiation surface of the subject 21.

(Scanning Probe 30)

The scanning probe 30 performs scanning along the first holding member50 by a scanning mechanism 31. This scanning mechanism 31 is controlledby a scanning control unit (not illustrated). The scanning probe 30includes an acoustic wave detector in which a plurality of detectionelements for detecting acoustic waves, such as piezoelectric elements,are arranged in an in-plane direction, a control unit of the acousticwave detector, and a housing. The scanning probe 30 can acquire signalsat a plurality of positions at one time. Scanning may be performed bythe scanning probe 30 in synchronization with the light-emitting timingof the light source.

(Probe 40)

The probe 40 includes an acoustic wave detector in which a plurality ofdetection elements for detecting acoustic waves, such as piezoelectricelements, are arranged in an in-plane direction, a control unit of theacoustic wave detector, and a housing. The probe 40 can acquire signalsat a plurality of positions at one time.

As an example, a representative element arrangement in which the probe40 is located above the scanning probe 30 will be described using FIGS.4A and 4B. FIGS. 4A and 4B are diagrams of the probe 40 viewed from thesubject through the first holding member 50. As illustrated in FIG. 4A,an element region 107, i.e., the acoustic wave detector of the probe 40,has a width substantially equal to a scanning range 106 of the scanningprobe 30. However, since the scanning range 106 of the scanning probe 30is wide, the number of elements of the probe 40 increases andconsequently processing time increases. Accordingly, in order to shortenthe processing time when the probe 40 has a large element arrangementwidth, the number of elements to perform processing may be reduced byselecting elements to operate. The method for selecting elements tooperate includes switching between ON/OFF of operations of elements bymeans of a detection circuit or switch. In addition, a sparse array typemay be used as the acoustic wave detector of the probe 40 as illustratedin FIG. 4B in order to shorten the processing time. Such elementarrangement can also be similarly adopted in cases other than the casein which the probe 40 is disposed above the scanning probe 30.

When the light source moves along with the scanning probe 30, positionsof elements to operate of the probe 40 may be selected in accordancewith a position from which light is radiated to the subject. Similarly,when a light source used by the probe 40 moves, elements for a positionfrom which light is radiated are selectively operated to performdetection.

The probe 40 may be positioned in the fixed manner as illustrated inFIGS. 4A and 4B or may be positioned so as to be able to perform ascanning operation.

In addition, the probe 40 may include characteristics, such as theelement width, the center frequency, and the element arrangement, thatare different from those of the scanning probe 30.

(Holding Members 50, 51)

The holding member is a flat plate member for stably maintaining theshape of the subject 21. The holding member can be used as a scanningpath of the scanning probe 30. For this reason, the holding member isarranged between the subject and the probe. When the subject isirradiated with light via the holding member, the holding member is amember through which light easily transmits. Additionally, the holdingmember is a member providing acoustic impedance matching between theliving body and the probe. Examples of the material of the holdingmember include, but are not limited to, a resin material, such aspolymethylpentene.

(Signal Collector 70)

The subject information acquisition device of this exemplary embodimentincludes the signal collector 70 that amplifies electrical signalsacquired by the scanning probe 30 and the probe 40, and converts theelectrical signals, i.e., analog signals, into digital signals. Thesignal collector 70 typically includes an amplifier, an A/D converter,and an FPGA (Field Programmable Gate Array) chip. When a plurality ofelectrical signals are acquired from the scanning probe 30 and the probe40, the signal collector 70 can process the plurality of signalssimultaneously, which can shorten the time for forming an image.

(Signal Processor 80)

A workstation or the like is typically used as the signal processor 80.Combining detected signals or pieces of image data and imagereconstruction are performed by means of software programmed in advance.For example, the software used in the workstation includes two modules,i.e., a combining module 81 configured to combine detected signals orpieces of image data acquired by the scanning probe 30 and the probe 40,and an image reconstruction module 82 configured to generate image datafrom the detected signals. In photoacoustic tomography, i.e., one kindof photoacoustic imaging, preprocessing, such as noise reductionprocessing, is performed on signals received at respective positionsprior to image reconstruction.

Examples of the algorithm to be used for image reconstruction performedby the image reconstruction module 82 include, but are not limited to,back projection in the time domain or Fourier domain, which is commonlyused in the tomography technology. When a large amount of time isallowable for image reconstruction, the image reconstruction method,such as inverse analysis using iteration, can be used.

In addition, in photoacoustic imaging, the use of a focused probepermits an image of the distribution of optical properties inside theliving body to be formed without image reconstruction. In such a case,it is not necessary to perform signal processing using the imagereconstruction algorithm.

Depending on circumstances, the signal collector 70 and the signalprocessor 80 are integrally formed. In this case, image information ofthe subject may be generated by means of hardware processing instead ofsoftware processing performed in a workstation.

(Display Device 90)

The display device 90 displays image data output from the signalprocessor 80. The display method to be used includes a method fordisplaying MIP (Maximum Intensity Projection) images, slice images, andso forth. In addition, the display device 90 can display athree-dimensional image in multiple different directions, and allows auser to change the tilt and displayed region of a displayed image andthe displayed window level and window width while checking the displayedimage.

The display device 90 may display a comparison of or difference betweenimage data combined by the signal processor 80 and pieces of image datato be combined by the signal processor 80. Also, the display device 90can change the emphasis level and the emphasis method of images measuredby different probes.

Second Exemplary Embodiment

FIG. 5 is a schematic diagram of a subject information acquisitiondevice according to a second exemplary embodiment.

In the subject information acquisition device according to thisembodiment, the probe 40 is positioned so that acoustic waves havingpropagated through the first holding member 50 are detected by the probe40. That is, the probe 40 is positioned to be in contact with thesubject 21 through the first holding member 50. Adopting such aconfiguration allows the probe 40 to perform scanning along a surface ofthe first holding member 50 when the probe 40 is of scanning type. Inaddition, when an acoustic matching material is used as the firstholding member 50, acoustic matching can be achieved between the probe40 and the subject 21. Furthermore, since the probe 40 detects acousticwaves via the first holding member 50 similarly to the scanning probe30, signals can be combined without delaying the signal. Therefore, theprocessing time required for combining signals can be shortened.

Third Exemplary Embodiment

FIG. 6 is a schematic diagram of a subject information acquisitiondevice according to a third exemplary embodiment.

In the subject information acquisition device according to thisembodiment, the probe 40 and the scanning probe 30 are positioned so asto face each other, and the probe 40 detects acoustic waves havingpropagated through the second holding member 51. If the subject 21 canbe held only with the first holding member 50, it is not necessary toprovide the second holding member 51.

Fourth Exemplary Embodiment

FIG. 7 is a schematic diagram of a subject information acquisitiondevice according to a fourth exemplary embodiment.

In the subject information acquisition device according to thisembodiment, the probe 40 and the scanning probe 30 are positioned suchthat a direction perpendicular to the detection surface of the probe 40is orthogonal to a direction perpendicular to the detection surface ofthe scanning probe 30. In photoacoustic imaging, a resolution in adirection perpendicular to the detection surface generally differs froma resolution in a direction horizontal to the detection surface. Since aresolution at a part where the detection regions of the scanning probe30 and the probe 40 overlap is superposition of the resolution in thedirection perpendicular to the detection surface of one of the probesand the resolution in the direction horizontal to the detection surfaceof the other probe, the resulting resolution generally increases.

In addition, the scanning probe 30 and the probe 40 may be positioned sothat the directions perpendicular to the detection surfaces of theindividual probes cross at an angle other than the right angle.

Fifth Exemplary Embodiment

FIG. 8 is a schematic diagram of a subject information acquisitiondevice according to a fifth exemplary embodiment.

In the subject information acquisition device according to thisembodiment, the probe 40 is positioned so as to at least partiallyfunction as the first holding-member support 60.

The probe 40 does not have to be entirely surrounded by another member,and instead, part of the probe 40 may be exposed from the other member.Furthermore, for example as illustrated in FIG. 9, the probe 40 may havea function of the first holding-member support 60. However, when theprobe 40 has a function of another member in this manner, a housing ofthe probe 40 has to be designed to be suitable as the other member.

In addition, the probe 40 may be positioned so as to at least partiallyfunction as any of the first holding member 50, the first holding-membersupport 60, the second holding member 51, the second holding-membersupport 61, and the patient support 63.

While exemplary embodiments have been described above, aspects of thepresent invention are not limited to these embodiments and encompassvarious modifications and applications as long as the modifications andapplications do not depart from the scope of the claims. Additionally,aspects of the present invention are applicable not only tophotoacoustic imaging but also to other kinds of imaging using acousticwaves.

According to the subject information acquisition device as describedabove, the shape of a subject may be stably maintained and high-qualityimages may be acquired.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of International Patent ApplicationNo. PCT/JP2011/072577, filed Sep. 30, 2011, which is hereby incorporatedby reference herein in its entirety.

The invention claimed is:
 1. A photoacoustic imaging device comprising:a patient support member having an upper support surface and configuredto support a patient in a prone position; a pair of holding plates, eachplate having a holding surface so as to sandwich a breast of the patienttherebetween; a movable probe located on one plate of the pair ofholding plates in opposition to a corresponding holding surface of another plate of the pair of holding plates, the movable probe beingconfigured to be movable along the one plate of the pair of holdingplates and configured to detect an acoustic wave generated at a firstregion of the breast and propagated through the one plate of the pair ofholding plates; a scanning mechanism configured to move the movableprobe along the one plate of the pair of holding plates so as to changea distance between the patient and the movable probe; a holding platesupport located beneath the patient support member and configured tosupport the one plate of the pair of holding plates; and a stationaryprobe provided to detect an acoustic wave generated at a second regionof the breast, wherein the holding plate support is located closer tothe patient support member than the movable probe so as to restrict anupper scanning region of the movable probe, and wherein the stationaryprobe is located between the patient support member and the holdingplate support such that the second region of the breast is locatedcloser to the patient support member than the first region.
 2. Thephotoacoustic imaging device according to claim 1, wherein thestationary probe is located closer to the patient support member thanthe movable probe so as to detect the acoustic wave generated at thesecond region of the breast not through the one plate of pair of holdingplates.
 3. The photoacoustic imaging device according to claim 1,wherein the stationary probe is located so as to face the movable probeand to detect the acoustic wave generated in the second region of thebreast and propagated through the other plate of the pair of holdingplates.
 4. The photoacoustic imaging device according to claim 2,wherein the stationary probe is located so as to detect the acousticwave generated in the second region of the breast and propagated throughthe one plate of the pair of holding plates.
 5. The photoacousticimaging device according to claim 1, wherein the stationary probe isfixed with respect to the breast.
 6. The photoacoustic imaging deviceaccording to claim 1, further comprising a signal processing unitconfigured to generate a first image data based on a signal detected bythe movable probe, generate a second image data based on a signaldetected by the stationary probe, and to generate combined image data ofthe first image data and the second image data.
 7. The photoacousticimaging device according to claim 1, wherein the stationary probeincludes an array of transducers arranged along a distant directionwhich a distance from the patient support member has a different value.8. The photoacoustic imaging device according to claim 7, wherein thestationary probe is configured to select some of the transducers tooperate among the array of transducers.
 9. The photoacoustic imagingdevice according to claim 6, wherein a center frequency of the movableprobe is different from a center frequency of the stationary probe, andthe signal processing unit is configured to match a resolution of thefirst image data and a resolution of the second image data and togenerate the combined image data after matching the resolution of thefirst image data and the resolution of the second image data.
 10. Thephotoacoustic imaging device according to claim 6, wherein the signalprocessing unit is configured to cause a display device to display acomparison between the combined image data, the first image data, andthe second image data.
 11. The photoacoustic imaging device according toclaim 1, further comprising a signal processing unit configured togenerate a combined signal of a signal detected by the movable probe anda signal detected by the stationary probe and generate image data basedon the combined signal.
 12. The photoacoustic imaging device accordingto claim 1, wherein the one plate of the pair of holding plates islocated between the movable probe and the breast, and the stationaryprobe is in direct contact with the breast.
 13. A photoacoustic imagingapparatus comprising: a first holding plate; a second holding platelocated so as to face the first holding plate and configured tointerpose a breast of a patient with the first holding plate; a movableprobe configured to detect an acoustic wave generated at a first regionof the breast and propagated through the first holding plate; a scanningmechanism configured to move the movable probe in a scanning range alongthe first holding plate to scan the first region of the breast; a firstholding-plate support configured to maintain the first holding plate ata patient side and to limit the scanning range of the movable probe; anda stationary probe located at a fixed position on the patient sidebetween the patient and the first holding-plate support out of thescanning range of the movable probe, the stationary probe configured todetect an acoustic wave generated at a second region of the breast, thesecond region is located closer to the patient side than the firstregion.